The present invention relates to portable radio terminals, particularly to a portable telephone as the portable radio terminal.
A portable telephone generally includes an antenna element to transmit and receive electromagnetic waves, and a radio transmitter-receiver provided in the portable telephone to apply energy to the antenna element. Since the impedance of the antenna element differs from the impedance of the radio transmitter-receiver, the impedance must be matched. Therefore, a matching circuit is provided between the radio transmitter-receiver and the antenna element in a conventional portable telephone for impedance matching.
FIG. 15 shows a structure of a conventional portable telephone. Referring to FIG. 15, a conventional portable telephone 401 includes a main unit case 410, a metal substrate 411, a feed unit 412, a matching circuit 413, a shield box 414, and a monopole antenna 421.
Metal substrate 411 is housed in main unit case 410. Shield box 414 is disposed at the surface of metal substrate 411, and matching circuit 413 constituting feed unit 412 is provided in the proximity of shield box 414. Monopole antenna 421 is connected to matching circuit 413.
Main unit case 410 is of a hollow configuration with metal substrate 411 located therein. Metal substrate 411 includes an epoxy glass material and a conductor layer 441a formed of copper at the surface thereof. Metal substrate 411 is of a rectangular configuration and has long sides and short sides.
Shield box 414 is provided at the upper portion of metal substrate 411. A radio transmitter-receiver is provided in shield box 414 to extract the information included in the wave received by monopole antenna 421 and to apply a predetermined energy to monopole antenna 421 to radiate waves. The radio transmitter-receiver is covered with shield box 414 to be shielded electromagnetically. Shield box 414 is configured, for example, by a layered body of copper and nickel with a nickel layer formed at the surface of copper.
Matching circuit 413 configuring feed unit 412 is provided so as to face a portion of shield box 414. Matching circuit 413 is formed of a lumped constant element such as coils and capacitors. Matching circuit 413 has a portion connected to the radio transmitter-receiver in shield box 414. The remaining portion of matching circuit 413 is connected to monopole antenna 421.
Monopole antenna 421 is attached to matching circuit 413 so as to extend in a predetermined direction. Monopole antenna 421 extends along the longitudinal direction of metal substrate 411 and main unit case 410. The electrical length of monopole antenna 421 is mainly set to xcex/4 or xcex/2.
The problem induced by such a conventional portable telephone 401 will be described hereinafter.
In general, when monopole antenna 421 receives a wave, a current flow is conducted from feed unit 412 to the radio transmitter-receiver in shield box 414. However, a current that flows at the surface of shield box 414 as shown by arrow 430 is also present. There is also a current that bypasses the surface of metal substrate 411 to flow to the radio transmitter-receiver. Since the conductivity of metal substrate 411 and shield box 414 is poor with respect to the antenna conductor, heat is generated at this area to result in signal loss.
The present invention is directed to solve such a problem. An object of the present invention is to provide a portable radio terminal that has a high antenna efficiency and improved in gain.
A portable radio terminal according to an aspect of the present invention includes a substrate, a shield member, an antenna element, and a feed unit. The substrate includes a portion having a conductive surface. The shield member covers a radio transmitter-receiver provided on the substrate to shield the radio transmitter-receiver electromagnetically, and has conductivity. The antenna element has an electrical length of (xcex/2)xc3x97N (N is an integer), and extends in a predetermined direction. The feed unit is provided at the substrate so as to be apart from the shield member in an extending direction of the antenna element, and includes a matching circuit connected to the antenna element.
In the portable radio terminal of the above structure, the feed unit is provided at the substrate so as to be apart from the shield member in the extending direction of the antenna element. Since the feed unit is apart from the shield member in the extending direction of the antenna element, the current flowing to the shield member can be reduced to prevent occurrence of a loss in electric signals. Thus, a portable radio terminal of high antenna efficiency and improved in gain can be provided.
Preferably, the end portion of the substrate is dielectric at the surface. The feed unit is provided at the portion of the substrate that is dielectric. Since there is no conductive portion where the feed unit is located, the current flowing to the conductive portion can be reduced. As a result, a loss in the electric signal can be prevented. Thus, a portable radio terminal of high antenna efficiency and improved in gain can be provided.
Also preferably, the end portion of the substrate has a protruding portion where the feed unit is provided. Since the feed unit provided at the protruding portion is immune to the effect of the shield member, a loss in electrical signals can further be prevented effectively.
Preferably, the shield member, feed unit and antenna element are provided sequentially so as to be distant from the substrate along the extending direction of the antenna element. Since the feed unit is provided apart from the substrate, the current flowing to the conductive portion can be reduced. As a result, a loss in the electric signal can be prevented. Thus, a portable radio terminal of high antenna efficiency and improved in gain can be provided.
A portable radio terminal according to another aspect of the present invention includes a substrate, a shield member, a dielectric, a feed unit, and an antenna element. The surface of the substrate is conductive. The shield member covers a radio transmitter-receiver provided on the substrate to shield the radio transmitter-receiver electromagnetically, and has conductivity. The dielectric is provided on the substrate. The feed unit is provided on the dielectric so as to be apart from the surface of the substrate in the thickness direction of the substrate, and includes a matching circuit. The antenna element has an electrical length of (xcex/2)xc3x97N (N is an integer), and is connected to the feed unit.
In the portable radio terminal of the above structure, the feed unit is provided on the dielectric so as to be apart in the thickness direction of the substrate""s surface. Since the feed unit is provided apart in the direction perpendicular to the surface of the substrate, the current flowing from the feed unit to the shield member or to the surface of the substrate can be reduced. As a result, a loss in electric signals can be prevented. Thus, a portable radio terminal of high antenna efficiency and improved in gain can be provided.